For persons who cannot benefit from traditional, air conduction hearing aids there are other types of sound transmitting hearing aids on the market, i e bone anchored hear ring aids which mechanically transmit the sound information to a persons inner ear via the skull bone by means of a vibrator. The hearing aid device is connected to an anchoring element in the form of an implanted titanium screw installed in the bone behind the external ear and the sound is transmitted via the skull bone to the cochlea (inner ear), i e the hearing aid works irrespective of a disease in the middle ear or not. The bone anchoring principle means that the skin is penetrated which makes the vibratory transmission very efficient.
This type of hearing aid device has been a revolution for the rehabilitation of patients with certain types of impaired hearing. It is very convenient for the patient and almost invisible with normal hair styles. It can easily be connected to the implanted titanium fixture by means of a bayonet coupling or a snap in coupling. Examples of this type of hearing aid devices are described in U.S. Pat. Nos. 4,498,461 and 5,735,790. It is also referred to the BAHA® bone anchored hearing aid marketed by Entific Medical Systems in Göteborg.
The previously known coupling devices for said hearing aids are all based on mechanically spring actuated parts. The disadvantage with such coupling details is the fact that they are exposed to mechanical wear so that in course of time there is a play in the system and other troubles when connecting the hearing aid device.